The present invention relates to a metal-flake, manufacturing apparatus which can simply and efficiently manufacture quenched metal-flake materials required for manufacture of thermoelectric materials, magnet materials, hydrogen absorbing alloys or the like.
Thermoelectric materials, magnet materials, hydrogen absorbing alloys or the like, which may be often intermetallic compounds, may be produced by crushing ingots. Conceived as an alternative way aimed at effective improvement of performances is to use quenched metal-flake materials, which way utilizes, as quench effects, compositional uniformity and crystal orientation along a quenching direction.
Such metal flakes are produced by preliminarily producing a continuous, wide-width thin strip and then crushing or shearing this continuous thin strip. Mainly used to produce such continuous thin strip is a single or double roll method.
In the single roll method, as illustrated in FIG. 1A, molten metal is ejected from a nozzle 2 arranged above a cooling roll 1 to stably keep a molten metal reservoir (puddle), using surface tension of the molten metal, on a top of the cooling roll 1 which contacts the molten metal, thereby producing a continuous, wide-width thin strip which is received in a storage box 3.
In the double roll method, as shown in FIG. 1B, just above a nip between two cooling rolls 4 which are arranged to contact with each other, molten metal is fed through a nozzle 5 and is solidified and rolled down between the cooling rolls 4, thereby producing a continuous thin strip which has been cooled at its opposite surfaces.
The single roll method, however, has a problem that the molten metal reservoir (puddle) is difficult to stably keep at the top of the cooling roll 1. If the molten metal is excessively ejected, the molten metal reservoir may become unstable and drop sideways or backward of the cooling roll 1 or get mixed with the thin strip product to thereby lower the uniformity of the finished product.
In the double roll method, on the other hand, the cooling rolls 4 are used not only for cooling and solidification operations but also for rolling-down operation so that a large drive power is required for the cooling rolls 4 and the cooling rolls 4 tend to be severely damaged.
Moreover, obtained as a product in either of the conventional methods is a continuous thin strip which is low in bulk density. Therefore, a large-sized storage box is required; alternatively, a separate crusher or shearing machine is required upstream of a storage box.
The present invention was made in view of the above problems of the prior art and has its object to provide a metal-flake manufacturing apparatus which can overcome the problem on stable supply of molten metal in the single roll method and the problem on roll-drive power in the double roll method and which can manufacture quenched metal-flake materials in a simple and highly efficient manner.
The inventors have reviewed quenched metal materials required for manufacture of thermoelectric materials, magnet materials, hydrogen absorbing alloys or the like to find out that utilized as quench effects in a thin strip are compositional uniformity and crystal orientation along a quenching direction and that to provide a continuous thin strip is not always a requisite since the thin strip is sheared or crushed in a next step. The invention was completed on the basis of such findings.
More specifically, in order to overcome the above problems, a plurality of cooling rolls are spaced to have a gap or gaps of a size greater than thickness of metal thin bodies to be produced. A nozzle is provided to eject molten metal onto a surface of such cooling roll. The first cooling roll quenches the molten metal from the nozzle into metal thin bodies. On the next cooling roll, the produced metal thin bodies are hit into flakes while the excess molten metal is made into metal thin bodies. Thus, freedom in supply of molten metal is enhanced and metal flakes can be stably and efficiently produced.
The cooling rolls are arranged at different heights so that the produced metal thin bodies are sequentially hit on the rolls, which increases chances of the produced metal thin bodies being hit on the cooling rolls and contributes to obtaining further finer flakes and changeability of the flake withdrawal direction.
Rotational axes of the cooling rolls may be out of parallelism so that a flying direction of the metal thin bodies, which is on a plane perpendicular to the rotational axis, may be changed with increased freedom.
Moreover, the cooling rolls may be arranged to rotate at different peripheral velocities. Differentiation in peripheral velocity between the cooling rolls will contribute to controlling the thickness of the metal thin bodies produced; if the cooling rolls with the same diameter were driven to rotate at the same peripheral velocity, thinner and thicker metal flakes would be produced on the upstream and downstream rolls, respectively.
In addition, the cooling rolls may have different diameters so as to have different peripheral velocities, which will contribute, just like the above, to controlling the thickness of the metal thin bodies.
The nozzle may have a plurality of nozzle openings along the axis of the cooling roll. Provision of the nozzle openings in the shape of, for example, slot or a circle, along the axis of the roll will contribute to further effective production of metal flakes.
The nozzle opening may have a sectional area of 0.7878-78 mm2. Even with the nozzle openings having the sectional area as large as of 28-78 mm2, which are unusually large as compared with those in the conventional production of metal flakes, thick metal flakes can be produced with higher efficiency. The shape of the nozzle openings are not limited to circle.
The nozzle and the cooling rolls may be placed in atmospheric gas and windbreak members may be arranged to prevent the atmospheric gas from being swirled by the rotating cooling rolls. Manufacturing in the atmosphere such as inert gas will enhance the quality of the metal flakes produced. Prevention of the atmospheric gas from being swirled by the rotating cooling rolls will prevent the nozzle-from being cooled and prevent the metal flakes from being scattered.
Furthermore, gas from atmospheric gas supply nozzles may be directed to guide the metal flakes towards a storage box in which metal flakes are to be stored, which will prevent the metal flakes from being scattered and contribute to efficient collection of the metal flakes in the box.
The storage box may have a cooler for cooling the collected metal flakes, which will contribute to further improvement of the metal flake cooling efficiency.